1. Field of the Invention
The present invention lies in the field of caliper type disc brakes wherein the brake may be alternatively under hydraulic or manual control.
2. Description of the Prior Art
One of the major difficulties in the utilization of caliper type disc brakes for the rear wheel(s) of a two or four wheeled vehicle is the problem of combining a mechanical, manually-operated brake control assembly to effect the requisite parking or emergency braking function.
Various prior art attempts to create such a combination have not been generally accepted because of the lack of an effective, simple and low-cost unit which can be readily adapted to existing disc brake designs. Examples of the prior art include U.S. Pat. Nos.: 3,185,263; 3,335,819; 3,337,008; 3,378,109 and 3,788,430.
U.S. Pat. No. 3,185,263 relates to a disc brake construction which employs a single control system which is operable under alternatively hydraulic or manual control. Basically, it incorporates the use of a pair of oppositely-disposed, hydraulically-separable pistons. The use of hydraulically separable pistons, under manual actuation of the brake elements, will tend to increase the gap between the pistons with the possibility of objectionable air aspiration into the hydraulic fluid in the cylinder. In an attempt to over this problem, a second embodiment is disclosed which makes use of a spring 238 positioned between the extremity 213 of the lever 211 used to manually actuate the brake. The spring 238 is used for maintaining piston 205 substantially stationary, irrespective of any motion of lever 211. However, following a certain number of spring flexures, it will fatigue and break. When this occurs, the air aspiration problem again presents itself. Additionally, it should be noted that this particular structural arrangement employs a substantial number of hydraulic fluid seals which are necessary to prevent leakage of the hydraulic fluid from its closed operational cavity. Still further, this particular arrangement does not include an automatic or self-adjusting mechanism to compensate for brake pad wear. Consequently, such adjustment must be made independently of the particular assembly disclosed therein.
Both U.S. Pat. Nos. 3,335,819 and 3,337,008 relate to disc brake assemblies which may be hydraulically or mechanically actuated. Fundamentally, these particular devices employ a modified hydraulic piston which interlocks with a manually operated lever to provide the desired parking or emergency brake function. The modified hydraulic piston possesses a bored-out portion with a series of sawtooth-like annular ridges therein. A radially expandable mating plug having a plurality of external gear teeth thereabout is adapted to fit loosely within the bored-out portion in its unexpanded condition and is immersed in the hydraulic fluid to protect it against fouling. The expandable plug is secured to a lever which, when actuated, causes the plug to adjustingly interlock the external gear teeth with the sawtooth ridges of the piston, thereby creating a mechanical link therebetween. Further actuation of the lever will thereafter force the piston into contact with the disc brake shoe thereby actuating the disc brake. Both of these arrangements are not only relatively complex, but are costly as well. Further, immersing the adjustment mechanisms in the hydraulic fluid creates the highly undesirable problem of contamination of the fluid as the intermeshing teeth wear against one another, especially during the actual adjustment phase.
U.S. Pat. No. 3,378,109 relates to a mechanical or manual brake assembly for use in conjunction with a caliper type disc brake. It operates separately and distinct from the hydraulically actuated disc brake.
U.S. Pat. No. 3,788,430 uses a radially-expandable plug similar to U.S. Pat. Nos. 3,335,819 and 3,337,008; however, its operation is quite different from the mechanisms shown in these patents. This arrangement is both complex and costly. Further, the brake wear adjustment mechanism is immersed in the hydraulic braking fluid which is highly undesirable as previously discussed.